The present invention relates to control of actuators in injection molding machines and other machines for optical disc substrata like CD or DVD, and more particularly relates to timing control of air blowing for releasing molded discs from a mold cavity or of air suction for holding them on the mold cavity.
A conventional sequence of operations in an injection molding machine is shown in FIG. 4. Auxiliary sequences such as advancing a gate cutter, blowing air for releasing molded discs from a mold cavity, and applying air suction for holding the discs in the mold, are started in accordance with main sequence timing of processes like mold closing and clamping, injection, cooling, mold opening, and ejecting.
Each process time or interval in both the main and auxiliary sequences is counted by timers or delay timers provided for each main and auxiliary sequence program. In the cycle of injection molding for DVD shown in FIG. 4, a timer for the cooling process starts to count after the mold cavity has been filled in with melted resin and held with holding pressure to complete an injection process.
At an arbitrary (e.g., predetermined or selected) time between the start of the holding-pressure process and the time of cooling is completed, a center aperture of the disc is formed with a gate cuter which advances into the hole of a gate insert bushing. To facilitate release of the solidified disc from the cavity surface of a stationary mold-half of the mold, and from the stamper surface on the mold cavity of a movable mold-half, passages for blown air are provided in the cavity side and the stamper side, respectively. At least one passage is provided in the movable mold-half for air suction to maintain the released disc on the mold cavity when the mold is opened.
The timing for blowing air from the various passages has to be set in consideration of the progress of solidification during the cooling of the molded disc. The timing of releasing the molded discs from the surface of the mold cavity and the stamper has a big influence on the birefringence of the finished discs and the appearance of cloud on the molded discs. Additionally, it is important for shortening the molding cycle time that molded discs are released from the cavity. as soon as solidified sufficiently that the molded disc is durable enough to take the ejecting force.
In conventional methods, each delaying timer used for timing the blowing air to release a molded disc from the cavity, or to leave it held by suction on the movable mold-half side, starts its count at the start of the cooling process in the main sequence. As it is very difficult to find the optimum cooling conditions by only one test molding, frequent modification of the cooling time set for the main sequences is required, especially when modification of completion time of the cooling process is frequently required.
In the conventional method, modifying the setting of the completion time for the cooling process causes the time set for each of the air blowing and suction timers to be modified. This is because the time for these delaying timers corresponds only with, or is a function of, the starting time of the cooling process in the main sequence. This results in increased work for adjusting each of the delaying timers.
To avoid this problem, one might think that the delaying timers might be made to correspond with the completion time of the cooling process, instead of the starting time of the cooling process. But if it were no pressure for air blowing or any suction could be applied until the end of the cooling process, because of the way the delaying timers function.
However, the timing of the air-blowing pressure and suction which are applied to the molded discs, and the time from completion of the cooling process to the start of mold opening, are influenced by the size of the injection machine or mold, the molding conditions, and the mold construction, which need to be considered accordingly. Inevitably, the starting times for air blowing and suction must be chosen to occur both before and after the completion of the cooling process.
In light of the above-mentioned problems, it is an object of the present invention to provide a novel control of the actuators which are used for auxiliary sequence processes, in which the actuators can adapt themselves to a modification of the process times of the main sequence.
It is another object of the present invention to provide a novel control of air blowing or suction actuators used for releasing molded discs in auxiliary-sequence processes, wherein the starting times of the processes in the auxiliary sequences can adapt themselves to a modification of the time T set for completing the cooling process of a main sequence.
It is another object of the present invention to provide a novel control for air blowing or suction actuators used for releasing molded discs in processes of an auxiliary sequence, wherein the starting time Txc2x1tn of the nth process in the auxiliary sequence for releasing a molded disc is operated by a CPU, wherein T is the time set for completing the cooling process of a main sequence and xc2x1tn indicates the set time, before or after the completion of interval T, to be output to each time counter for operating the respective actuator or actuators.
For a better understanding of the operation, objects and advantages of the invention, reference should be had to the accompanying drawing and description in which there is illustrated and described a preferred embodiment of the invention.